Integrated Taxonomic Revision of Afrotropical Xyleborinus (Curculionidae: Scolytinae) Reveals High Diversity After Recent Colonization of Madagascar

Abstract

The ambrosia beetle genus Xyleborinus Reitter, 1913 is particularly species rich in Madagascar where the genus exhibits extraordinary morphological variation not seen elsewhere. This study provides the first detailed molecular phylogeny of the genus based on COI, 28S, and CAD gene fragments. Biogeographical and taxonomic hypotheses were tested for the Afrotropical fauna with a particular focus on the Malagasy radiation. Analyses revealed a single colonization of Madagascar no earlier than 8.5–11.0 Ma, indicating an extraordinary recent radiation on the island which has given rise to at least 32 species. Two recolonization events of the African mainland were strongly supported by the molecular data, with several other intraspecific dispersals to the mainland inferred from species distributions. A taxonomic re-evaluation of all Afrotropical Xyleborinus resulted in several taxonomic changes. We found that morphological differences associated with COI divergence higher than 7% indicated different species. Twelve new species are described: Xyleborinus castriformis Eliassen & Jordal, sp. nov., Xyleborinus clivus Eliassen & Jordal, sp. nov., Xyleborinus concavus Eliassen & Jordal, sp. nov., Xyleborinus coronatus Eliassen & Jordal, sp. nov., Xyleborinus diadematus Eliassen & Jordal, sp. nov., Xyleborinus laevipennis Eliassen & Jordal, sp. nov., Xyleborinus magnispinosus Eliassen & Jordal, sp. nov., Xyleborinus margo Eliassen & Jordal, sp. nov., Xyleborinus ntsoui Eliassen & Jordal, sp. nov., Xyleborinus singularis Eliassen & Jordal, sp. nov., Xyleborinus tuberculatus Eliassen & Jordal, sp. nov., and Xyleborinus turritus Eliassen & Jordal, sp. nov., all from Madagascar. New synonyms are proposed for Xyleborinus aemulus (Wollaston, 1869) [=Xyleborinus spinifer (Eggers, 1920)], Xyleborinus andrewesi (Blandford, 1896) [=Xyleborinus mimosae (Schedl, 1957)], Xyleborinus dentellus (Schedl, 1953) [=Xyleborinus forcipatus (Schedl, 1957)], Xyleborinus octospinosus (Eggers, 1920) [=Xyleborinus mitosomipennis (Schedl, 1953)], and Xyleborinus similans (Eggers, 1940) [=Xyleborinus sclerocaryae (Schedl, 1962)]. Two species were given new status: Xyleborinus profundus (Schedl, 1961) is elevated from subspecies of Xyleborinus aduncus (Schedl, 1961), and Xyleborinus mitosomus (Schedl, 1965) is reinstated from its previous synonymy with Xyleborinus spinosus (Schaufuss, 1891). Xyleborus gracilipennis Schedl 1957 is reverted to its original genus, and a similar status is confirmed for Xyleborus collarti Eggers 1932. The number of taxonomically valid Xyleborinus species in the Afrotropical region is now 47, which includes 3 adventive species. Revised diagnoses for all species and a key for species identification are provided.